What does "round corner" and "square corner" refer to when it is used to identify modern US definitives?

Question

Catalogs differentiate between several U.S. definitives issued between 1999 and 2006 by the words "square corner" and "round corner." What should I look for to tell the difference between these stamps? I can't find a definition of these terms anywhere!

Answer 1

A 'square corner' is exactly what it sounds like - the corner is squared off at a right angle. A 'rounded corner' is, well, rounded - like the corner of most computer keys (and keyboards); it doesn't have a distinct point.